Powder reactor including a perforated conical grid



Aug. 21, 1956 E. w. BRANDT POWDER REACTOR INCLUDING A PERFORATED CONICALGRID Filed March 2, 1954 ulnumuml INVENTOR MMM/ww ATTORNEY United StatesPatent O POWDER REACTR INCLUDING A PERFORATED .CONICAL GRID EdgarWilliam Brandt, Geneva, Switzerland, assigner' to Anstalt fur dieEntwicklung von Eriindungen und gewerblichen Anwendungen Energa, Vaduz,Liechten stein, a corporation of Liechtenstein Application March `2,1954, Serial No. 413,537

I,Claims priority, application Switzerland March '14, 1953 Il Claim.(Cl. 60-35.6)

This invention relates to powder reactors for selfpropelled projectiles.

There are two distinct types of self-propelled projectiles viz: (a)those which undergo a reaction thrust over a considerable part of theirtrajectory, such as for example aircraft rockets, and (b) projectilesred with the aid of a launching weapon and propelled practically onlywhile travelling through the tube in which they are guided.

While the rst type of projectile can attain a high speed because it isaccelerated during a relatively long period, the second, withouttravelling at the same speeds, has less dispersion because on thecessation of the thrust at the muzzle of the weapon it complies with thesame ballistic conditions as an ordinary projectile.

The present invention relates more particularly to reactors forself-propelled projectiles of the second type hereinbefore set forth,preferably utilizing double-base colloidal powders having a high speedof combustion and developing pressures of the order of 200 to 300 kg.per sq. cm.

It is known to be advantageous to select for the propulsion of suchprojectiles particles of powder the geometric shape of which tends tokeep the combustion surface approximately constant. Numerous shapes havebeen proposed, 'among which preference is often given to tubularparticles assembled in bundles in the reactor; use may also be made of asingle (tubular or multitubular) shaped body.

For the purpose of reducing the duration of combus tion of a givenpowder charge, while increasing the maximum pressure resulting therefromin the reactor, it is necessary to increase the total ignition surfaceof the particle or particles, and consequently at the same time theirstructural fragility. As the pressure may attain its maximum value inonly one or two hundredths of a second, it is obvious that a shock isproduced on the dilerent parts of the charge, which tends to disrupt theelements. Experience shows that, all other conditions being equal, thisinitial phenomenon also depends on the method of ignition and theposition of the igniter in relation to the self-propulsion charge.

Moreover, the fragility of the particles increases during the combustionof the powder in parallel layers, so that iinally the powder tube ortubes are broken up in an unforeseen and irregular manner. The variationof pressure as a function of `time is therefore no longer a reproduciblefunction and the law of propulsion is no longer constant lfrom oneprojectile to another.

Furthermore, the nozzle or nozzles of the reactor may be partiallyclosed by the particles of powder, which even during a very shortperiod, is sucient to create asymmetry of propulsion which isdetrimental to `accuracy of re, if it occurs when the projectile hasissued from the muzzle of the weapon. It should also be noted thatparticles of powder, carried by the reactor gases, are ejected from thenozzle or nozzles and that these unburnt 2,759,326 Patented Aug. 21,1956 ICC particles which escape combustion give rise to a considerablereduction of the self-propulsion output.

Finally, the unburnt particles give rise to another no less seriousinconvenience, since hitherto the operator using a tiring weapon of theBazooka type for tiring such projectiles, at maximum speeds of the orderof 200 to 250 meters per second, has been compelled to protect his faceand hands specially with the aid of cumbersome accessories (shield ordeflector, gloves, etc.) because in order that a self-propelledprojectile may attain these speeds, its charge must burn over a fewmetres in front of the muzzle of the weapon.

lt has already been proposed to obviate the aforedescribed disadvantagesby incorporating in the reactor a grid or" suitable shape, adapted toretain and iilter the unburnt particles. Previously known grids howeveronly incompletely solved this problem. lf, in fact, the apertures of thegrid are of too great a diameter, it fuliills its function imperfectly,allowing the ltration therethrough of particles of smaller diameter,while orifices of small diameter are liable to be obstructed on theignition of the charge and thus to give rise to irregular combustion andasymmetrical ejection of the gases.

The powder reactor of the present invention is of the type comprising acylindrical reservoir housing a self-propulsion charge, a pyrotechnicigniter of high caloric power, one or more nozzles at the end of saidreservoir, and a metallic grid of generally conical shape widening fromrear to front, interposed between the charge and the nozzle or nozzles,and is characterized in that said grid, perforated by a large number oforifices of small diameter, axially encloses at its narrowest part theigniter which is held at a distance from -said charge, for the purposeof irst heating the parts of Ithe grid which delimit its or-iiices andthen to burn by contact .the particles of powder thus filtered.

The length of the igniter is preferably much smaller than that of thegrid, the rear end of the propulsion charge being supported at the levelof the base of said grid, which is at that point of a diameterapproximately equal to that of the reservoir, so that, at the time oftiring, the gases from the igniter can expand without risking damage tothe particles of powder, which they ignite by sweeping over a maximumsurface of their rear section. Moreover experience has shown that thecombination of an igniter having a high caloriiic power with the gridsuch as hereinbefore deiined, permits the retention and the lburning ofparticles of small diameter. ln addition, the reactor of the .presentinvention gives rise to additional pressure which entails an increasedspeed of combustion and consequently a reduction of the total durationof the reaction.

According to one embodiment of the invention, the grid has at leastfifteen oriiices per square centimetre, the diameter of each orificebeing smaller than two mill-imetres, Afor a reaction pressure lyingbetween 200 and 300 kg. per sq. cm. In order to prevent hindrance to theflow of the gases, the grid must haveat least `six hundred orilices.

As 'the result of repeated tests it has been found that the particles ofdimensions smaller than the diameter hereinbefore speciiied appear innegligible quantity in the propulsion gases and that they are burnedduring their travel between the grid and the mouth of the nozzle ornozzles, after having passed Kthe neck Where the temperature of thegases is highest.

The small aperture of the oriiices hereinbefore defined (less than 2millimetres in diameter) prevents the deiiec- .tion of the ignitionflame towards the exterior of the grid, which would not fail to occurwith oriiices of greater diameter.

T-he conicity of the grid, measured by the angle of a generatrix to Vtheaxis,may, in accordance with the invention be between 3 and 10 degrees,at which value the inclination tof the internal surface of the grid isparticularly favorable for the combustion of unburnt particles. In fact,those particles which,` after having encountered the widened part of thegrid, are too large to be consumed instantaneously, are brought, whileburning, by the inclination of t-he f-ace of said grid towards a zone ofsmaller diameter, thus reducing the risk of obstruction of the orifices.

The active surface of the grid being a function of its conicity, ofwhich the limits are suitable to the pressures normally -required of 200to 300 kg. per sq. cm., could nevertheless be increased if it were foundadvantageous to increase the pressure with a view to making availablehigher acceleration of the projectile on leaving the weapon.

In order to enable the invention to be more readily understood,reference is made to the accompanying drawings, which illustratediagrammatical-ly and by way yof example, one embodiment thereof, and inwhich:

Fig. l -is a diagram illustrating variations of pressure as a functionof time;

lFig. 2 shows in axial section lthe rear part of a reactor in accordancewith the invention.

In the diagram illustrated in Fig. 1, the curve (in broken lines)indicates the pressure of combustion plotted against time in thereservoir of a conventional powder re-actor. The second curve (solidline) shows .the corresponding variation of pressure inside a reactor ofthe type illustrated in Figure 2, the conditions of the experiment beingthe same in both cases tand the reactors differing only through theirgrids and ythe respective arrangements of the igniter and the propulsivecharge in relation to said grid.

Itis found that the reactor of the invention gives rise in its reservoirto a maximum pressure P2 yfhich is greater than, the maximum pressure P1of .a reactor of conventional type, fwhile the corresponding reactiontime t2 is shorter than t1.

The reactor illustrated in Figure 2 comprises a cylindrical reservoir 1,a self-propulsion charge constituted by a bundle of tubular grains 2arranged in the form of a crown (an additional central grain can, ifdesired, also be provided). The grains 2 are perforated transversely at3 Y- in order to promote equilibrium of pressures during combustion.

A grid 4 `of generally conical form, truncated near its apex andwidening from rear to front, is interposed between the charge 2 and aplug 5 comprising a group of t convergent-divergentnozzles 6. Thenarrowed part 7 of the grid 4 is held by compression in a hollow 8 ofthe plugl 5, while its base has anedge 9 .in the periphery of whichcorresponds to the internal calibre of the .reservoir 1. A part of theannular rear portion of each grain 2 bea-rs on `the edge 9, which servesas support. An axial igniter 10, the rear end of which is housed in ametallic casing 11', which itself isV screwed into the plug S, issurrounded by the narrowed part 7 of the grid 4.

The length of the igniter 10 penetrating into the grid 4 issubstantially less than that of the grid and preferably does notexceedfhalf the length of said grid, The result is that the greater partof the internal lvolume of the grid is clear and that a relativelyconsiderable free space separates the igniter 10 from the powder grains2.

The 'orifices 13 of the grid 4, are in an actual construction on thesame scale far more numerous and there will be at least l5 of them persquare centimetre, the diameter of each being less than 2 millimetres.This condition is particularly satisfactory for the propulsion of areactor operating under maximum pressures of the order of 200 to 300 kg.per sq. cm. Tes-ts carried out with a grid the internal diameter ofwhich, at the base of the cone, measured about 40 millimetres and theheight of the active part of which was twice as great, showed that ithad to have at least 600 orifices such as those hereinbefore defined andpreferably more than 1,000 orifices.

The conicity of the grid 4, that is to say the angle a subtended by itsaxis with one of its generatrices, is 6 or 7 degrees, but may varyaccording Ito the conditions of operation (combustion pressure,dimensions of the reservoir, ete), while preferably remaining withinlimits comprised between 3 and 10 degrees.

Finally, the nozzles 6 of the powder reactor are closed by an annularwad 15 adapted to yield under a determined pressure, marking thecommencement of propulsion. As the reactor described is moreparticularly intended to propel a projectile, it also comprises afinning constituted by an assembly of fins 16. A detonating primer lf2,projecting from the rear of the plug 5, is adapted to communicate fireby mechanical percussion to the igniter 10 containing a pyrotechniccomposition having a high calorifi'c power, for example analuminothermic mixture.

On firing the shot, and as the result of the percussion of thedetonating primer 12, the igniter 10 deagrates and the jet of fireissuing from it, guided by the internal surface of the grid 4,penetrates between and through the tubular grains 2, igniting each ofthem. by their internal and external surfaces, and also by their rearportion. This process permits the initial heating of the grid by theigniter and facilitates combustion by Contact of the unburnt particleswhich encounter it subsequently. The small diameter of the orifices 13of the grid 4 prevents the jet of re issuing from the igniter 10 frompenetrating, even partially, into the compartment 14 provided betweenthe external surface of the grid 4 and the wall of the reservoir 1.

The propulsion gases issuing from the grains 2, and also the particlesof powder which they may carry, encounter the grid 4, which stops theunburnt particles and permits the penetration of the gases throughorifices 13 into the compartment 14. As soon as the pressure hasattained a sufficient value, the wads 15 yield and the gases pass intothe nozzles.

What I claim is:

A powder reactor for rockets of the type comprising a cylindricalchamber containing a propelling charge, a pyrotechnic igniter. of highcaloritic power, a series of nozzles at the rear of said chamber, ametallic grid of generally conical shape, widening from rear to frontinterposed between the charge and the nozzles, said grid having a-largenumber of orifices of small diameter and enclosing said igniter axiallyin its narrowest part, the rear end of the propelling charge beingsupported on the wider front end of said grid which at that point is ofa diameter approximately equal to that of said chamber.

References Cited in the file of this patent UNITED STATES PATENTS2,605,607 Hickman Aug. 5, 1952

